Fluid or hydraulic mountings include a fluid which augments isolation and/or damping characteristics that may be achieved in elastomer mountings alone. This augmentation may take the form of adding additional damping or added inertial forces. Fluid mountings are generally described in LORD.RTM. Technical Article LL-2166 entitled "Understanding Hydraulic Mounts for Improved Vehicle Noise, Vibration and Ride Qualities" by W. C. Flower. Commonly assigned U.S. Pat. No. 4,811,919 to Jones describes a fluid mounting which incorporates a volume compensator. Other examples of fluid mountings and dampers may be found in commonly assigned U.S. Pat. No. 5,413,320 to Herbst, U.S. Pat. No. 5,374,039 to Schmidt et al., U.S. Pat. No. 5,127,607 to McGuire, and U.S. Pat. No. 5,197,692 to Jones et al., U.S. Pat. No. 5,540,549, to McGuire and U.S. Pat. No. 5,501,434 to McGuire. Fluid mountings are, in essence, tunable passive devices which use a fluid to add additional damping or tuned-fluid "inertia" effects. In all these devices, compensation of fluid expansion, pressurization, and fill to remove gas bubbles is a problem. However, prior art methods of accomplishing these feats have involved utilization of multi-component systems which tend to add unwanted cost and complexity. In particular, it is very important in aggressive fluid mounting applications, such as in fluid pylon isolators, that no gas bubbles are present in the operating chambers. In essence, relative movement between the inner and outer member will cause any bubble present to expand and contract instead of moving the fluid between the chambers. This degrades performance. Further, reliable methods of providing pressurization to minimize cavitation of the fluid at high relative motions is required.
Therefore, there is a recognized need for more effective and cost efficient methods of compensation, pressurization, and fill in fluid mounts.